The invention relates to a spectrometer comprising a light source for exciting a sample, a motor-adjustable monochromator, a secondary electron multiplier connected to an adjustable operating voltage source, with, on its output side, an A-D converter, and a computer which stores the output signals thereof and the associated wavelength and which controls the position of the monochromator and which regulates the operating voltage source of the secondary electron multiplier in accordance with a stored relationship between the operating voltage and the spectral sensitivity of the spectrometer, with the wavelength of the radiation as adjusted at the monochromator.
A spectrometer of that kind is disclosed in U.S Pat. No. 4,373,813 and can be used for example to determine the percentage content of various chemical elements in the sample, as the output signal level of the secondary electron multiplier, when the monochromator is set to a spectral line which is characteristic in respect of a given chemical element, is a direct measurement of the amount of the element in question, in the sample.
As the width of a spectral line is only about one three hundred thousandths of the spectrum between about 2000 and 6000 .ANG., such spectrometers require monochromators with a high degree of resolution in order to be able to separate closely adjacent lines from each other and provide a clear association with a given wavelength. Suitable monochromators with a degree of resolution of up to 1.6 millions of points (with respect to a rotary movement of 360.degree.) are available on the market. It is also known from U.S. Pat. No. 3,868,499 for the monochromator of a spectrometer to be caused to pass through the spectrum in a computer-controlled mode, for which purpose the monochromator is provided with a stepping motor and a position detector.
For certain uses of spectrometry, for example for spectral analysis to determine the composition of a metallurgical sample, very wide measuring ranges of for example 0.001% to 100% content are required, with at the same time a high degree of measuring accuracy of 0.5 parts per thousand (with respect to the aboslute value). The spectrometer of the general kind set forth in the opening part of this specification cannot cover such a measuring range and cannot achieve such a degree of accuracy as, having regard to the necessary noise signal ratio, with a given operating high tension (with respect to a given spectral range), the secondary electron multiplier produces a useful output signal at most over the range of three decimal powers, that is to say, it only covers a measuring range of from example 0.01% to 10%.
The invention is based on the problem of providing a spectrometer of the kind set forth in the opening part of this specification, which permits time-saving and fully automatic recording of the spectrum emitted by a sample, with an increased measuring range and an enhanced degree of measuring accuracy.